In search of the solution to the world energy crisis, researchers and industry have focused their efforts on harnessing energy from alternative energy sources, most notably the sun, wind, and ocean waves.
Technologies for harvesting energy from these sources are in their infancy, though significant progress has been made. However, the efficiency of existing technologies is limited, and resulting environmental issues, such as noise and microclimate change, have become increasingly problematic. Unless these technologies can be dramatically improved, their energy harvesting potential will be limited. High governmental priority has been assigned to improving these technologies. The focus so far has been to engineer more efficient devices (e.g. blades and turbines) that convert wind and surface wave energy into electricity and to improve solar panel design.
Little attention is being paid to harnessing the vibration energy that is created by natural dynamic environmental processes and by manmade processes, both of which represent vast pools of renewable mechanical energy. Natural dynamic environmental processes (wind, ocean waves, subsurface ocean currents, tectonic movement) cause the vibration of structures with which they come into contact. Vibration is also created in almost all manmade processes. It results from all forms of transport, in the vehicles themselves, and from vehicular contact with roads, bridges, train tracks and other infrastructure. Technologies for harvesting these alternative power sources are in their infancies. Vibration energy harvesters (VEH) are a logical way to convert this vibration and convert it to electrical energy.
The state-of-the-art of VEH, as measured by patent applications and awards, are limited to micro-electro-mechanical systems (MEMS) that are only capable of generating very small amounts of power measures in the order of milliwatts. The development of a technology based on a VEH that is capable of harvesting a measurable percentage of the total energy in vibrating structures (VS) deserves attention. Accepting the possibility of such a device, its development would allow for harvesting a substantial percentage of the total energy is VS, using a system comprising a moderate number of devices integrated with and distributed throughout the VS. Such a system would harness the vast mechanical energy pools created in the natural world by first converting the energy as vibration in structures designed for this purpose. One advantage of this novel approach is that the integration of the VEH as part of the VS isolates all moving parts from the potentially hostile environment that is the source of vibration. Structures can be designed to capture the mechanical energy in subsurface ocean currents and in deep ocean internal waves. Another advantage this novel approach is that the coherence of the source of mechanical energy being tapped need not be as great as that required by a wind turbine, for example. Structures can be designed to capture energy from atmospheric turbulence.
The invention comprises a VEH capable of harvesting a measurable percentage of the total energy in vibrating structures.
The use of vibration energy harvesters (VEH) comprised of multiple oscillators attached to a base that is in turn attached to a vibrating structure (VS), is known in the art. The use of vibration dampers (VD) comprised of multiple oscillators encapsulated in a housing element that is in turn attached to a VS, is also known in the art. Accepting that the base/housing-element is rigid, its motion does not depend on the locations of the oscillators; the geometric distinction is, therefore, irrelevant.
The invention is distinguished over the existing arts by the different objectives, numbers of oscillators, and the relative massiveness of the devices. For example, VEH typically have a small to moderate number of oscillators; say, less than 10, which VD of the type related to the invention typically have a much larger number; say, greater than several 100's, even 1000's. Another distinction is known VEH have vastly smaller sizes and masses; U.S. Pat. No. 6,858,970 B2, for example, describes a MEMS harvester with mass- and size-ratios, relative to those of the VS, that approach infinitesimals. By contrast, effective VD have mass- and size-ratios, relative to those of the VS, which while still small relative to 1, are finite.
Because of their small mass, known VEH are severely limited in the quantities of energy harvested, typically measured at the level of milliwatts; U.S. Pat. No. 6,858,970 B2 is representative of the art of VEH. At the milliwatt level, the total quantity of energy harvested in any reasonable time is a vanishing percentage of the energy available in the VS. The principal application of currently known VEH is to power micro-sized sensors and computers, with an understanding that the rate of energy extraction from the VS is too small to have an effect on the vibration field in the structure. The design of the MEMS energy harvester is consistent with these applications.
Rescaling the mass of an available VEH can result in a comparable rescaling of the quantity of energy harvested, but only if the more massive device initiates an energy transfer within the VS, drawing energy from locations remote from that of the device, to the device. Without this energy transfer, only the energy in the immediate neighborhood of the device, a percentage of the total energy available that approaches an infinitesimal, is available of harvesting. Significantly, the initiation of the energy transport process requires certain quantifiable design criteria, not known to the present art, be met. The invention includes the identification of these criteria, expressed by a limited number of device parameters, and a design framework for determining the values that result in an effective device.
Mechanical devices for damping the vibrations of a structure are designed to either change the dynamics of the structure, thereby precluding the introduction of energy, or to dissipate the energy as heat. Damping devices based on a large number of oscillators encapsulated in a housing element are in the latter category. Typically, the mass of an efficient VD is a large enough percentage of that of the VS to negatively impact design criteria for the VS not related to the VD. Pub No: US 2009/0078519 A1 describes a class of VD that accomplishes the damping by a much less massive device than heretofore known. The design according to this known device results in the rapid transfer of a significant percentage of the energy drawn into the device, to the internal oscillators wherein it “remains trapped indefinitely,” using the terminology in the reference. The indefinite trapping of energy in the oscillators largely eliminates the need for internal “energy dissipaters” that add mass to the device. The design requires that the oscillator resonances densely fill a frequency band according to a formularization, i.e. a prescribed dependence of the values of the resonant frequencies relative to one another. The dense filling requirement is expressed by a minimum number of oscillators, which is also determined by a formularization. Both formularizations are essential to this known device.
While the present invention is presented as a vibration energy harvester, the observation that a significant quantity of the available energy is removed from the VS suggests it also has a role as a VD. In this role, the invention is distinguished from the class described in Pub. No: US 2009/0078519 A1 by the active removal of energy transferred to and entrapped within the internal oscillators, by converting it to electricity. Thus, the “near irreversibility” of the vibration damper described in Pub. No: US 2009/0078519 A1 is made “absolute” in the case of the present invention, by the removal of the energy transferred to the interior oscillators, as electricity. This active removal of energy fundamentally changes the device design and fabrication, by eliminating the need for the formularization that determines precise values for the oscillator resonances relative to each other. Eliminating this formulation eliminates a major complexity in the fabrication of the present device.